The present invention relates to a soft magnetic alloy strip long in length manufactured by a single roll method, in which strip warpage in widthwise direction of the strip is small and superior surface characteristics of the strip are obtained, a magnetic member using the soft magnetic alloy strip, and a manufacturing method of the soft magnetic alloy strip.
A soft magnetic alloy strip such as amorphous alloy, nano-crystalline alloy or the like manufactured by the single roll method is used for a variety of transformers, choke coils, sensors, magnetic shields or the like because of its superior soft magnetic characteristics. As a typical material, a Fexe2x80x94Cuxe2x80x94(Nb, Ti, Zr, Hf, Mo, W, Ta)xe2x80x94Sixe2x80x94B based alloy or a Fexe2x80x94Cuxe2x80x94(Nb, Ti, Zr, Hf, Mo, W, Ta)xe2x80x94B based alloy or the like disclosed in JP-B-4-4393 (U.S. Pat. No. 4,881,989) is known. A nano-crystalline soft magnetic alloy is a finely crystallized alloy, and the grain size thereof is about 50 nm or less with good soft magnetic characteristics, in which nano-crystalline alloy thermal instability as found in the amorphous alloy scarcely occurs, and it has high saturation magnetic flux density similar to that of Fe-based amorphous alloy, superior soft magnetic characteristics, and low magnetrostriction. Further, it is known that the nano-crystalline soft magnetic alloy is small in change occurring with the elapse of time, and is superior in temperature characteristics.
The single roll method is superior to a method such as a twin roll method in mass productivity, and thus, becomes currently dominant regarding a manufacturing method of an amorphous alloy strip or another amorphous alloy strip for nano-crystalline alloy. FIG. 1 is a schematic view showing an example of a single roll device. A base alloy is melted in a nozzle made of ceramics or quartz, and is pressurized at a pressure p. Then, an alloy melt is ejected from a nozzle slit onto a cooling roll that is rotating at a high speed, and is quenched very rapidly, thereby manufacturing an amorphous alloy strip of about 2 to 100 xcexcm. The amorphous alloy strip and an amorphous alloy strip for nano-crystalline alloy are produced from a common alloy strip used as a starting material. Therefore, in the present invention, both of these strips are herein-below referred to as a soft magnetic alloy strip.
It is known that the soft magnetic alloy strip produced by the single roll method is required to be cooled as fast as possible to thereby be lowered in temperature in order to prevent the strip from being crystallized and/or embrittlement of the strip.
In addition, in a case where a soft magnetic alloy strip is wider in width, the strip comes into intimate contact with the cooling roll, and it is required to forcibly peel the strip off the roll. With respect to this peeling position, it is generally thought that, since the temperature of the strip is lowered as it is spaced apart from a portion immediately beneath the nozzle, a preferable peeling position is deemed to be one distant as far as possible in view of the generation of amorphous structure or the prevention of embrittlement.
However, in actual manufacture, because of various conditions, there is produced only a strip which is greatly warped in widthwise direction, and moreover which is broken shortly in the longitudinal direction. The warped strip causes a problem that, in the case where the warped strip is wound and laminated, it is difficult to handle the strip, and in the case where a winding magnetic core or laminated magnetic core is manufactured, open spaces occur between the strips, which causes reduction in space factor. In addition, in the case where strip is required to be slit, the strip short in length causes a problem that the times of setting the short strip to a slitter are increased with the result that the cost thereof increases. Further, the warped strip causes another problem that, when the warped strip is forcibly flattened and used, the stress is likely to remain with the result that soft magnetic characteristics are deteriorated.
On the other hand, it is known that air pockets occur, due to entrainment of air, on the strip surface (hereinafter, referred to as xe2x80x9ca roll contact facexe2x80x9d) which is in contact with roll. FIG. 2 is a schematic view showing dimensions of the air pockets occurring on the roll contact face. This air pocket is generally a recess having a shape extended in the longitudinal direction of the strip. Thus, when this strip is used for a magnetic core, it will cause reduction of the space factor. Thus, it is important to reduce the number of air pockets as small as possible. However, in mass production for manufacturing a much amount of wide strip, superior magnetic characteristics which should occur inherently cannot be obtained insofar as mere reducing of the number of air pockets and mere reducing of an area rate of the air pockets are concerned.
It was found that the influence of these warps and/or air pockets become significant in the case where mass production of Fexe2x80x94(Cu, Au)xe2x80x94Mxe2x80x94Sixe2x80x94B based or Fexe2x80x94(cu, Au)xe2x80x94Mxe2x80x94B based amorphous alloy strip wide in width which is a base material of a Fe-group nano-crystal soft magnetic alloy strip is performed. In addition, even if the strip is used for a magnetic core or the like in amorphous state, it is found that there occurs a problem that the magnetic characteristics at a low frequency are particularly deteriorated due to crystallization of the air pocket portion.
It is an object of the present invention to provide a wide, less warped soft magnetic alloy strip long in length manufactured by the single roll method as a soft magnetic alloy strip with reduced air pocket size and with reduced recess on the roll contact face side, and further, a magnetic member with its improved space factor and soft magnetic characteristics using this strip and a manufacturing method of the soft magnetic alloy strip.
The inventors found out the factors of the occurrence of warpage of the soft magnetic alloy strip and of the occurrence of air pockets at the time of the manufacturing thereof, and succeeded in restricting the warpage and air pockets to particular degrees, whereby solving the foregoing problem. First, warpage of the strip also occurs in the longitudinal direction of the strip, however, attention is focused on the warpage in widthwise direction here. As regards a strip narrow in width, widthwise warpage hardly causes problem, however, it becomes serious if manufacturing condition is not proper in a case of a wide strip. In particular, warpage occurs more remarkably in the case where the thickness of the strip is thin. As regards a soft magnetic alloy strip preferably employed for various magnetic members such as magnetic core, it is preferred for the warpage to be limited in a range not more than 0.2xc3x97d mm in widthwise direction of the strip when the strip has a width of d mm, and further it is preferred for the strip to have such a long, successive length as to be not less than 50 m. In addition, when the thickness of this strip is 25 xcexcm or less and the width d is 10 mm or more, and further, even when the thickness of the strip is 20 xcexcm or less and the width d is 20 mm or more, it is preferred for the degree of the warpage to be limited to the range defined above.
In conventional manufacturing conditions, it is impossible to obtain a strip having the degree of warpage and length both limited above. For example, if a roll temperature is too low, it has been found that the strip warps. This reason is not well understood, however, it is presumed that the solidification of molten alloy occurs in the vicinity of a nozzle at a time when the molten alloy ejected from the nozzle solidifies on a roll to thereby become amorphous and the temperature distribution of the resultant strip relates to this warpage. In addition, it has been found out that, if a distance between a portion of a strip immediately beneath the nozzle and the peeling-off point of the strip is not appropriate, the strip breaks during the production of the strip wide in width, so that continuous, long strip cannot be manufactured.
According to the first aspect of the invention, there is provided a soft magnetic alloy strip produced by a single roll method in which a molten alloy is ejected onto a rotating, cooling roll from a nozzle having a slit and in which the surface temperature of the cooling roll after the elapse of 5 seconds or more after the molten metal was ejected is maintained to be not less than 80xc2x0 C. but not more than 300xc2x0 C. while performing the peeling-off of the alloy strip at a distance ranging from 100 mm to 1500 mm when measured from a position of the outer circumference of the roll just beneath the nozzle slit along the circumference of the roll, whereby it becomes possible to produce a soft magnetic alloy strip of a continuous length not less than 50 m in which warpage is restricted to be not more than 0.2xc3x97d mm (which xe2x80x9cdxe2x80x9d is the width of the strip). In a case where magnetic cores or the like are manufactured by using this strip, it is possible to manufacture the magnetic cores or the like having high dimensional precision, high space factor, and superior soft magnetic property. Incidentally, these warpages are prescribed in a strip state after production of the amorphous alloy strip, not warpage occurring after heat treatment or working or using for a magnetic core.
Another aspect of the invention relates to surface characteristics of a roll contact face. The invention has been achieved from the findings that, when roll temperature rises during the strip manufacture, each of air pocket portions each having a large size is crystallized with the result that the magnetic characteristics are deteriorated and that, unless surface roughness Ra correlating with a depth of a recess of an air picket is reduced, the magnetic characteristics are deteriorated.
That is, a soft magnetic alloy strip having the width of the air pockets of not more than 35 xcexcm on the roll contact face, the length of the air pocket of not more than 150 xcexcm and the centerline average roughness Ra of not more than 0.5 xcexcm on the roll contact face is preferred in the view of superior soft magnetic characteristics and good space factor.
The inventors have further found out that the surface characteristics of the roll contact face are particularly important from the viewpoint of the magnetic performance. In this respect, the inventors have found that molten metal-ejecting pressure, a peripheral speed of the cooling roll and an interval between the cooling roll and a nozzle tip end are important during the production of the strip. That is, the alloy melt is ejected on the rotating cooling roll made of a metal from a nozzle having a slit, and an alloy strip is manufactured by the single roll method, wherein molten metal-ejecting pressure during the ejecting of the molten metal is controlled to be 270 gf/cm2 or more, the peripheral speed of the cooling roll being controlled to be 22 m/s or more, and preferably, an interval between the cooling roll and the nozzle tip end is made to be not less than 20 xcexcm but not more than 200 xcexcm, so that the strip can be manufactured with high quality, high stability, and in mass production.
Although many air pockets on the roll control face are caused and vary in size, the width of the air pockets prescribed in the invention is the largest width (W) in the air pockets when measured within the range of 0.4 mmxc3x970.5 mm on the roll contact face, and a length of air pockets is the longest length (L) in the air pockets when measured within the range of 0.4 mmxc3x970.5 mm on the roll contact face. W and L are defined schematically in FIG. 2. Further, the centerline average roughness Ra of the roll contact face is a value defined by making the cut-off value xcexc prescribed in JIS B 0601 be 0.8 in the widthwise direction of the soft magnetic alloy strip and by making measurement length be at least 5 times the cut-off value.